Patent GB-1455620-A (GB)
Title: Subscribers selector panel for use with wire television  distributing networks
IPC: H04N7/10
Filed: 1974-10-14
Abstract: 1455620 Wired broadcasting; frequency changing; tuning arrangements; digital-to-analogue conversion OFFICE DE RADIODIFFUSION-TELEVISION FRANCAISE and R MAUDUECH 14 Oct 1974 [12 Oct 1973] 44422/74 Headings H3Q H3T H4R and H3H A subscriber's selector panel for cable television comprises an input isolating stage 1, Fig. 2, a mixer 3 and a local, oscillation generator 2 comprising two voltage-controlled oscillators, the beat frequency of which constitutes the local oscillations, the oscillators being controlled by a transcoder receiving decimal signals. The input stage 1 comprises transistor 100 with a collector load resistor 117 in series with tuned circuit 118, 119. To inductor 118, is coupled inductor 118 2  tuned by capacitor 120 whereby F.M. signals are applied to outlet 12, and also inductor 118 3  tuned by capacitor 121, whereby V.H.F. signals are applied to outlet 13. The collector of transistor 100 is coupled to the base of isolating transistor 123, the collector of which is coupled via lines 208, 218 to the emitter of mixed transistor 30: this is in common base connection and feeds the U.H.F. outlet via a tuned transformer comprising coupled lines 32. The voltage-controlled oscillators comprise transistors 200, 210 respectively each with an emitter circuit resistor 206, 216 respectively and feedback between collector and emitter over capacitors 207, 217 respectively. The collector circuits comprise parallel resonant lines 202, 212 respectively, coupled to lines 208, 218 respectively and tuned by varactor diodes 201, 211 biased over resistors 426, 436 respectively from respective D.C. amplifiers 424, 434 : each of these has feedback over a network comprising resistors 425, 435 respectively and resistors 420-423 and 430-433 respectively. Each of the latter resistors is connected via an isolating diode to an appropriate output in either the units register 411u or tens register 411d. The desired channel is selected by means of a keyboard 400 providing a coded combination of four binary digits by transcoder 401: in addition a pulse from OR gate 402 is fed to device 403 which removes button rebound oscillations and imparts steepness to the wavefront. Device 404 fed with D.C. from power supply 51 provides a wavefront R 3  used for return to zero of the logic system. Device 403 produces two signals B, and # the latter slightly out of phase with B: signals # and R 3  are fed to AND gate 405 the output of which feeds input one of flip-flop 406, the zero input of which receives signal B. Flip-flop 406 produces a signal T, Fig. 3 corresponding to pressure on one of the keys 400. A channel number comprises two decimal numbers whose order of origin must be known; for this purpose flip-flop 407 furnishes a signal at its output one for the first number and at its zero output for the second number. The signal T is applied to monostable 408 the output E of which controls AND gates 409, 410 whose second inputs are connected to respective outputs of flip-flop 407: the output Ed of gate 409 indicates the ten numeral and the output Eu from gate 410 the unit. The four binary numerals corresponding to the tens decimal numeral are fed in parallel to the tens register 411d and the four corresponding to ones to the units register 411u : register 411d is returned to zero by the signal R z  and register 411u by a signal R zu  derived from AND gate 412 which receives signal R z  and an inverted signal Ed from inverter 413. The combinations displayed by the registers 411d, 411u are decoded in decoder 42-43, each of the resistors 420-423 and 430-433 being traversed by a current depending upon whether the corresponding logic function is one or zero. The arrangement is such that when the television receiver, connected to terminals 7, is switched on a relay 50 is energized to close its contacts and so energize the reflector panel.